This study will begin a re-examination of the psychobiology of N,N-Dimethyltryptamine, an endogenous hallucinogen. Careful recruitment of experienced hallucinogen users will precede the development of a DMT rating scale, developed by interviewing experienced DMT users & modified after administration of a high dose of DMT to 10 subjects. Lower doses also will be administered to develop dose-response curves to the neuroendocrine cardiovascular and autonomic effects of this compound.